In many applications, noise-shaping techniques are used to increase an apparent signal-to-noise ratio in a frequency range. Examples come from many fields of technology, for instance fields comprising digital or other quantized signal processing.
For instance, in many transmitter, receiver or transceiver applications, one or more local oscillator (LO) signals are used for up-mixing or down-mixing a signal to be transmitted or received, respectively. To reduce distortions more and more frequency synthesizers based on digital phase-locked loops (DPLLs) have become an important approach because they may allow a greater flexibility and an easier configurability for creating multiple local oscillator signals for multiple bands.
In this field, digital-to-time converters (DTCs) are becoming a more and more attractive approach for the generation of local oscillator signals in multi-standard radio-frequency (RF) transmitters, receivers or transceivers as they may benefit from the digital design flow including the possibility of RF synthesis. To name just one example, DTC-based transceiver architectures may be used in protocols, where carrier aggregation (CA) is used and where multiple local oscillator signals may have to be generated by a single radio frequency DPLL driving multiple DTCs. Such a DPLL- and/or DTC-based frequency synthesizer may allow a more robust operation with respect to distortions and a higher integration.
However, a DTC often quantizes with a finite number of levels, which may result in visible spurs in the spectrum. Moreover, in a digital DTC also the number of bits available may limit the spectral performance. To fulfill certain spectral requirements imposed, for instance, by the application, the protocol to be used or other implementation details, noise-shaping techniques may be used. However, conventional noise-shaping techniques may negatively influence the spectral response of such a system, for instance, at specific sensitive frequencies or frequency bands.
Therefore, a challenge exists to improve an overall noise performance of such a system.
However, not only in the field of transmitters, receivers or transceivers, similar challenges exist. They exist in many fields of signal processing, for instance, comprises digital audio processing, digital image processing, digital video processing, analog/digital conversion and similar technical applications and fields.